diff --git a/go/types/check_test.go b/go/types/check_test.go
index 3f6ed83181..21ad03c58e 100644
--- a/go/types/check_test.go
+++ b/go/types/check_test.go
@@ -45,6 +45,7 @@ var (
 
 // Each tests entry is list of files belonging to the same package.
 var tests = [][]string{
+	{"testdata/cycles.src"},
 	{"testdata/decls0.src"},
 	{"testdata/decls1.src"},
 	{"testdata/decls2a.src", "testdata/decls2b.src"},
@@ -205,7 +206,7 @@ func checkFiles(t *testing.T, testfiles []string) {
 	ctxt.Check(pkgName, fset, files...)
 
 	if *listErrors {
-		t.Errorf("--- %s: %d errors found:", pkgName, len(errlist))
+		t.Errorf("--- %s: %d errors found", pkgName, len(errlist))
 		for _, err := range errlist {
 			t.Error(err)
 		}
diff --git a/go/types/expr.go b/go/types/expr.go
index c0d8028255..f69b7e4c9f 100644
--- a/go/types/expr.go
+++ b/go/types/expr.go
@@ -116,13 +116,13 @@ func (check *checker) collectParams(scope *Scope, list *ast.FieldList, variadicO
 	return
 }
 
-func (check *checker) collectMethods(list *ast.FieldList) (methods []*Func) {
+func (check *checker) collectMethods(list *ast.FieldList, cycleOk bool) (methods []*Func) {
 	if list == nil {
 		return nil
 	}
 	scope := NewScope(nil)
 	for _, f := range list.List {
-		typ := check.typ(f.Type, len(f.Names) > 0) // cycles are not ok for embedded interfaces
+		typ := check.typ(f.Type, cycleOk)
 		// the parser ensures that f.Tag is nil and we don't
 		// care if a constructed AST contains a non-nil tag
 		if len(f.Names) > 0 {
@@ -140,15 +140,23 @@ func (check *checker) collectMethods(list *ast.FieldList) (methods []*Func) {
 			}
 		} else {
 			// embedded interface
-			utyp := typ.Underlying()
-			if ityp, ok := utyp.(*Interface); ok {
-				for _, m := range ityp.methods {
+			switch t := typ.Underlying().(type) {
+			case nil:
+				// The underlying type is in the process of being defined
+				// but we need it in order to complete this type. For now
+				// complain with an "unimplemented" error. This requires
+				// a bit more work.
+				// TODO(gri) finish this.
+				check.errorf(f.Type.Pos(), "reference to incomplete type %s - unimplemented", f.Type)
+			case *Interface:
+				for _, m := range t.methods {
 					check.declare(scope, nil, m)
 					methods = append(methods, m)
 				}
-			} else if utyp != Typ[Invalid] {
-				// if utyp is invalid, don't complain (the root cause was reported before)
-				check.errorf(f.Type.Pos(), "%s is not an interface type", typ)
+			default:
+				if t != Typ[Invalid] {
+					check.errorf(f.Type.Pos(), "%s is not an interface type", typ)
+				}
 			}
 		}
 	}
@@ -1042,7 +1050,7 @@ func (check *checker) rawExpr(x *operand, e ast.Expr, hint Type, iota int, cycle
 				check.errorf(obj.pos, "illegal cycle in declaration of %s", obj.name)
 				x.expr = e
 				x.typ = Typ[Invalid]
-				return // don't goto Error - need x.mode == typexpr
+				return // don't goto Error - want x.mode == typexpr
 			}
 		case *Var:
 			x.mode = variable
@@ -1494,7 +1502,7 @@ func (check *checker) rawExpr(x *operand, e ast.Expr, hint Type, iota int, cycle
 
 	case *ast.InterfaceType:
 		x.mode = typexpr
-		x.typ = NewInterface(check.collectMethods(e.Methods))
+		x.typ = NewInterface(check.collectMethods(e.Methods, cycleOk))
 
 	case *ast.MapType:
 		x.mode = typexpr
diff --git a/go/types/testdata/cycles.src b/go/types/testdata/cycles.src
new file mode 100644
index 0000000000..3e10873d01
--- /dev/null
+++ b/go/types/testdata/cycles.src
@@ -0,0 +1,112 @@
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cycles
+
+type (
+	T0 int
+	T1 /* ERROR "cycle" */ T1
+	T2 *T2
+
+	T3 /* ERROR "cycle" */ T4
+	T4 T5
+	T5 T3
+
+	T6 T7
+	T7 *T8
+	T8 T6
+
+	// arrays
+	A0 /* ERROR "cycle" */ [10]A0
+	A1 [10]*A1
+
+	A2 /* ERROR "cycle" */ [10]A3
+	A3 [10]A4
+	A4 A2
+
+	A5 [10]A6
+	A6 *A5
+
+	// slices
+	L0 []L0
+
+	// structs
+	S0 /* ERROR "cycle" */ struct{ _ S0 }
+	S1 /* ERROR "cycle" */ struct{ S1 }
+	S2 struct{ _ *S2 }
+	S3 struct{ *S3 }
+
+	S4 /* ERROR "cycle" */ struct{ S5 }
+	S5 struct{ S6 }
+	S6 S4
+
+	// pointers
+	P0 *P0
+
+	// functions
+	F0 func(F0)
+	F1 func() F1
+	F2 func(F2) F2
+
+	// interfaces
+	I0 /* ERROR "cycle" */ interface{ I0 }
+
+	I1 /* ERROR "cycle" */ interface{ I2 }
+	I2 interface{ I3 }
+	I3 interface{ I1 }
+
+	I4 interface{ f(I4) }
+
+	// testcase for issue 5090
+	// TODO(gri) fix this
+	I5 interface{ f(I6) }
+	I6 interface{ I5 /* ERROR "unimplemented" */ }
+
+	// maps
+	M0 map[M0]M0
+
+	// channels
+	C0 chan C0
+)
+
+func _() {
+	type (
+		t1 /* ERROR "cycle" */ t1
+		t2 *t2
+
+		t3 t4 /* ERROR "undeclared" */
+		t4 t5 /* ERROR "undeclared" */
+		t5 t3
+
+		// arrays
+		a0 /* ERROR "cycle" */ [10]a0
+		a1 [10]*a1
+
+		// slices
+		l0 []l0
+
+		// structs
+		s0 /* ERROR "cycle" */ struct{ _ s0 }
+		s1 /* ERROR "cycle" */ struct{ s1 }
+		s2 struct{ _ *s2 }
+		s3 struct{ *s3 }
+
+		// pointers
+		p0 *p0
+
+		// functions
+		f0 func(f0)
+		f1 func() f1
+		f2 func(f2) f2
+
+		// interfaces
+		i0 /* ERROR "cycle" */ interface{ i0 }
+
+		// maps
+		m0 map[m0]m0
+
+		// channels
+		c0 chan c0
+	)
+}
\ No newline at end of file